dungtd wrote:

Each shelf of a bookcase contained 12 books. If the librarian took out 21 books and rearranged the remaining books so that all shelves but one contained 8 books and the last shelf contained 11 books, how many shelves does the bookcase have?

(C) 2008 GMAT Club - m09#13

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Gmatclub manager,

Should the question be "the librarian took out 21 books and rearranged the remaining books so that each shelf contained 8 books and the last shelf contained 11 books"?

Thanks !

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The wording in the question is correct . If the "but one" is omitted like you mentioned, the details contradict with each other. If each shelf contains 8 books,last shelf also must contain 8 books and can't contain 11 books.

The "but one" indicates that each shelf except the last shelf has 8 books and the last shelf has 11 books.

Here is how we can solve the problem.

Let x be the number of shelves.

No of books in the beginning =12*x

After taking out 21 books No of remaining books = 12x -21

when the remaining books are rearranged, each shelf except the last shelf has 8 books and the last shelf has 11 books. So No of remaining books is also equal to 8*(x-1)+11

12x-21=8(x-1)+11

4x=24

x=6. Answer B

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